1. Field of the Invention
The present invention relates to a mask forming method and a semiconductor device manufacturing method used in lithography process of semiconductor process.
2. Description of the Related Art
In recent years, the downsizing of semiconductor devices has been in progress. As a result, in a mask manufacturing process, a correction process for correcting an optical proximity effect (OPC: Optical Proximity Correction) has been carried out. By the OPC process, fine graphics such as fine pattern steps or fine pattern irregularities are formed on design data.
Mask pattern data at the time of forming a mask pattern (data obtained by applying a required process such as an OPC process for design data) includes data that corresponds to fine graphics.
However, fine graphics are not always reflected faithfully on a pattern (mask pattern) actually formed on a mask. Therefore, the degree of faithfulness of a mask pattern relevant to mask pattern data (degree of pattern forming faithfulness) is lowered at a portion of the mask pattern that corresponds to the fine graphics.
In recent years, a mask pattern has been inspected at a high sensitivity of defect detection. Thus, there has been established a situation in which the lowered degree of pattern forming faithfulness cannot be ignored in guaranteeing an inspection result.
For example, in a mask defect inspection of Die-to-Database comparison method (Jpn. Pat. Appln. KOKAI Publication No. 2002-23345), the following problem occurs due to the lowered degree of pattern forming faithfulness.
In the mask defect inspection of the Die-to-Database method, the presence or absence of a defect in a mask pattern is checked with a desired sensitivity of defect detection by comparing the mask pattern and mask pattern data with each other.
Here, in the case where, due to the lowered degree of pattern forming faithfulness, a difference between the mask pattern and the mask pattern data exceeds a critical condition (thresholds indicating whether or not a defect is observed) for the severest defect detection sensitivity (corresponding to a detected minimum defect size) at a portion of the fine graphics formed by OPC process, the portion of the fine graphics formed by OPC process is recognized as a defect.
The above described defect is a harmless defect from the viewpoint of device guaranteeing (hereinafter, referred to as a false defect). There is no need for correcting the false defect. For this reason, a work of classifying a plurality of detected defects into false defect and true defect (harmful defect from the viewpoint of device guaranteeing) is carried out.
In this classifying work, a workload increases due to a trend for downsizing semiconductor devices. Part of the classifying work is automated. However, the automated classifying work is still poor in reliability. Therefore, there has not been established a situation in which a classifying work by visual inspection can be eliminated.
Under such a situation as described above, a tremendous number of false defects occur in one mask due to the downsizing of a pattern and due to the downsizing of an OPC correction grid (correction unit). Specifically, false defects may occur in number exceeding an upper limit of defects in number that can be maintained (stored) in a defect inspection apparatus. In this case, there has been established a situation in which the whole mask cannot be inspected.
An inspection capable of reducing the number of detected false defects includes a mask defect inspection by Die-to-Die comparison method. This inspection selectively extracts regions formed by the same pattern group from the all of patterns formed on one mask, and comparatively checking detection signals between the extracted regions, thereby detecting a defect.
However, in general, a pattern forming region of one mask is not formed of only the same pattern group, and all the defects in a desired region of the mask cannot always be detected by only the defect inspection of the Die-to-Die comparison method.